Wow... i'm almost surprised to see how this is simple, and yet very detailed in the middle. It looks great. The tree looks very good. I would say your colour choice is very interesting - it's not the colour combination we'd normally see, yet it looks suitable. Nice work.
PS- you have a pixel wide white border on the left hand side (and right I think - it's hard to see) and at the top. I doubt it was intentional, but I think it would be better if you made it consistent and either removed it, or added it to the bottom edge as well. ^^
